Pope Benedict's decision to send a Vatican delegation to a United Nations conference on racism has opened a new rift in relations with Jewish groups, which fear it will be used as a platform to attack Israel.

"By participating, the Vatican has given its endorsement to what is being prepared there (against Israel)," Rome's chief rabbi, Riccardo Di Segni, told the Italian newspaper La Stampa.The United States and some of its allies, including Italy -- a country which often sees eye-to-eye with the Vatican at international conferences -- are boycotting the meeting.

On Sunday the pope, who makes his first trip to Israel as pontiff next month, called the conference an important initiative and said he hoped it could help "put an end to every form of racism, discrimination and intolerance".

Shimon Samuels, head of the European office of the Simon Wiesenthal Centre, said the Vatican "is giving a seal of approval in the hate campaign" against Israel.

"This is not a position on which one can hedge," Samuels said. "You can't have it both ways. The Vatican is a powerful voice and (a boycott) could have had a strong demonstrative effect."

Chief Vatican spokesman Father Federico Lombardi defended the Vatican's presence and said a disputed conference text had been improved in recent weeks.

"This is an international conference promoted by the United Nations and the Holy See. Just because some important countries are not attending does not mean that the Holy See cannot have a positive and constructive dialogue there," Lombardi said.

U.S. President Barack Obama, who is expected to hold his first meeting with the pope in July, said Washington feared the conference would be a venue for antagonism towards Israel.

Israel recalled its ambassador to Switzerland on Monday in protest. Diplomats walked out of the conference when Iranian President Mahmoud Ahmadinejad accused Israel of establishing a "cruel and repressive racist regime" over Palestinians.

Di Segni, the Rome rabbi, said the pope's decision was "the latest imprudent step" in his relations with Jews, which were severely strained earlier this year over the pope's decision to lift the excommunication of a bishop who denied the Holocaust.

The United States and Israel walked out of the last major U.N. race conference in Durban, South Africa, in 2001 after Arab states tried to label Zionism as racist.